And once the chip was read, how could I tell if the circuit was open or closed?
= = =
There are several options for you here, according to the engineers at Brady Corp. Option 1 would be something like a tamper-evident RFID tag, with which you could change a bit of memory based on physically modifying a tag or antenna. The challenge here would be that tamper-evident solutions typically operate one-way (i.e. once a tag is altered, it cannot be returned to original state).
Option 2 would involve encoding a tag’s EPC or user memory in real time to reflect the current state of a switch or circuit being open or closed. That would require a using dedicated RFID reader to interface with some other system to identify a switch or circuit being open or closed, then writing the appropriate value to the tag. When the tag was read, that value would represent “open” or “closed,” based on what was last written to the tag’s memory.
Could RFID Enable a Temperature-Triggered Circuit to Open? »